Field of the Invention
The present invention relates to an image reading apparatus, e.g., a scanner, which is configured to read an image (hereinafter referred to as “original image”) of an original.
Description of the Related Art
An image reading apparatus is provided in an image forming apparatus, e.g., a copier or a multifunction apparatus, and is used to read an original image in copying or facsimile transmission. Moreover, the image reading apparatus may be connected to an information processing apparatus, e.g., a personal computer, and be used as a scanner. The image reading apparatus may include an original conveying apparatus, e.g., an automatic document feeder (ADF). The image reading apparatus including the original conveying apparatus is configured to continuously take in originals from the original conveying apparatus one by one, and to continuously read original images while conveying the taken-in originals. The image reading apparatus can effectively read the original images by continuously taking in the originals from the original conveying apparatus.
To read an original image, the image reading apparatus irradiates an original being conveyed with light, and receives reflected light from the original. The image reading apparatus converts the received reflected light into an electric signal to generate image data representing the read original image. The image reading apparatus reads the original image by irradiating the original with light assuming that a direction perpendicular to a conveying direction of the original is a main scanning direction. When the original is conveyed with inclination with respect to the main scanning direction, the image reading apparatus reads the original image in an inclined state. In order to correct the inclination of the original image, there is proposed an image reading apparatus configured to detect the inclination of an original being conveyed and to conduct inclination correction (US Patent Application Publication No. 2009/0185240). Further, there is proposed an image reading apparatus having enhanced reliability in detection of an edge part of the original image conducted when an inclination amount of the original image is detected (Japanese Patent Application Laid-open No. 2013-123119). The image reading apparatus disclosed in Japanese Patent Application Laid-open No. 2013-123119 is configured to read an image having an area wider than an original and to detect the inclination amount of the original image by inferring the area of the original image by analogy from a reading result based on a size of the original and a detection result of the edge part of the read image.
When dust, a stain, or the like adheres to a background part of the original, the image reading apparatus reads the dust, the stain, or the like in the background part as an image. When detecting the edge part of the original image from the image including the dust, the stain, or the like, the image reading apparatus sometimes erroneously recognizes the dust, the stain, or the like as the edge part of the original image. The erroneous recognition of the edge part of the original image inhibits the inclination amount of the original from being detected accurately. The present invention has a primary object to provide an image reading apparatus capable of recognizing the edge part of the original image with high precision even when dust, a stain, or the like adheres to the background part and accurately detecting the inclination amount of the original.